And they say their concept - using laser light to entice the
body's own stem cells into action - may offer enormous promise
beyond just dentistry in the field of regenerative medicine.

The researchers used a low-power laser to coax dental stem cells to
form dentin, the hard tissue similar to bone that makes up most of a
tooth, demonstrating the process in studies involving rats and mice
and using human cells in a laboratory.

They did not regenerate an entire tooth in part because the enamel
part was too tricky. But merely getting dentin to grow could help
alleviate the need for root canal treatment, the painful procedure
to remove dead or dying nerve tissue and bacteria from inside a
tooth, they said.

"I'm a dentist by training. So I think it has potential for great
impact in clinical dentistry," researcher Praveen Arany of the
National Institute of Dental and Craniofacial Research, part of the
U.S. National Institutes of Health, said on Friday.

Arany expressed hope that human clinical trials could get approval
in the near future.

"Our treatment modality does not introduce anything new to the body,
and lasers are routinely used in medicine and dentistry, so the
barriers to clinical translation are low," added Harvard University
bioengineering professor David Mooney. "It would be a substantial
advance in the field if we can regenerate teeth rather than replace
them."

Using existing regeneration methods, scientists must take stem cells
from the body, manipulate them in a lab and put them back into the
body. This new technique more simply stimulates action in stem cells
that are already in place.

Scientists had long noticed that low-level laser therapy can
stimulate biological processes like rejuvenating skin and
stimulating hair growth but were not sure of the mechanisms.

Arany noted the importance of finding the right laser dose, saying:
"Too low doesn't work and too high causes damage." High-powered
lasers are used for cutting and cauterizing.

The researchers found that laser exposure of the tooth at the right
low intensity prompted certain chemically active, oxygen-containing
molecules to activate a cell protein known to be involved in
development, healing and immune functions.

This protein in turn directed stem cells present in tooth pulp to
turn into dentin. Stem cells are master cells that are capable of
transforming into various types of tissues in the body.

The researchers drilled holes in the molars of the rodents, zapped
the tooth pulp with the laser and put on temporary caps, then
watched as dentin formed over a period of 12 weeks.

The question is whether using this method could get other stem cells
to became useful in laser-induced regenerative medicine. Arany said
he was hopeful it could be used in healing wounds, regenerating
cardiac tissue, dealing with inflammation issues and fixing bone
damage, among other applications.